Manufacture of nodular iron



March 23, 1957 c. R. LOPER, JR., ETAL 3,311,469

MANUFACTURE OF NODULAR IRON Filed April .25, 1964 FOI OUKDOQ 5225 BEzoSou 350m Eeomuxmm Sou 0250a 83 e 0 For 350m INVENTORS CARL R. LOPER JR.BY RICHARD W.HEiNE United States Patent 3,311,469 MANUFACTURE OF NODULARIRON Carl R. Loper, Ira, and Richard W. Heine, both of Madlson, Wis.,assignors, by mesne assignments, to Union Carbide Corporation, acorporation of New York Filed Apr. 23, 1964, Ser. No. 362,056 2 Claims.(Cl. 75-130) The present invention relates to the manufacture of nodulariron. More particularly, the present invention relates to an improvedprocess for increasing the proportion and amount of truly spheroidalgraphite in nodular llODS.

In the production of nodular iron castings, to obtain a high qualityproduct, it is required that, during the solidification of the iron, anadequate number of graphite spheroids be nucleated and caused to growuniformly as solidification progresses in order to depress the formationof carbides and undesirable graphitic shapes such as vermiculargraphite.

In the past, in efforts to achieve this effect, magnesium has been usedas an addition to induce the formation of spheroidal graphite andsilicon has been used as a graphitizing innoculant. However, in the useof these materials, metal temperature and the carbon equivalent(C=percent C+ /3% Si) and carbon contents of the base metal have had tobe rather closely controlled. Moreover, even using very closelycontrolled processing conditions, the results have not been entirelysuccessful as regards the total amount of truly spheroidal graphiteproduced, the elimination of undesirable vermicular graphite, and theprevention of carbide formation.

It is therefore an object of the present invention to provide a processfor the production of nodular iron in which the amount of spheroidalgraphite is substantially increased.

It is another object of the present invention to provide a process whichsubstantially eliminates the presence of carbides in nodular iron.

It is a further object of the present invention to provide a processwhereby vermicular graphite is substantially eliminated from nodulariron.

It is another object of the present invention to provide a process whichpermits the use of lower temperatures in the casting of nodular iron.

It is a further object of the present invention to provide a processwhich permits lower carbon equivalent irons, e.g., 4.3-4.4, to be castwithout the formation of vermicular graphite or carbides.

Other objects will be apparent from the following description and claimsin conjunction with the drawing which graphically and comparativelyillustrates advantages of the present invention.

A process in accordance with the present invention to achieve theaforementioned objects comprises bringing together molten iron,magnesium and bismuth.

In the practice of a particular embodiment of the present invention, abath of molten iron containing from about 3.5 to 5.0% carbon equivalentis prepared and to this iron bath is added magnesium, for example in theform of magnesium-ferrosilicon, and bismuth, which can conveniently bein lump form. A practical manner of making the magnesium and bismuthaddition is to place the magnesium-ferrosilicon and bismuth in a pocketat the bottom of a ladle and pouring molten iron onto the material inthe pocket. Subsequently, the thus treated molten iron can betransferred to a pouring ladle and ultimately cast into suitable shapes.

In the present invention, the molten iron should contain from about 3.5to about 5.0% carbon equivalent, which can derive partly by way of theferrosilicon addition. This carbon equivalent is necessary in order'toproduce a spheroidal graphite cast iron which will graphitize duringsolidification.

Silicon in an amount from about 1% to 5% should also be present in thebase iron in order to cause graphite formation. The silicon can beinitially present in the base metal or it can be added wholly or partlyin the form of ferrosilicon innoculant following conventional practice.

The magnesium addition should range from about 0.02 to 0.25% by weightof the iron and the bismuth addition ranges from very small amounts,suflicient to provide an increase in spheroidal graphite, up to 0.1%.

As little as 0.0001% bismuth addition will provide a substantialincrease in the amount of spheroidal graphite compared to the amountproduced using magnesium without bismuth.

An industrially convenient range for the bismuth addition to providesignificant advantages is from 0.0005 to 0.050%, a preferred range forthe bismuth addition is from about 0.01% to about 0.015%.

In order to demonstrate the effectiveness of bismuth as an addition inthe manufacture of nodular iron, various tests were performed ashereinafter described.

The metal used in the tests was commercial iron and was melted in abasic cupola. A 1500 lb. mixing ladle was arranged in front of thecupola and lb. transfer ladles, having a pocket in the bottom, were alsoprovided.

Treatment of the base metal involved placing a predetermined amount ofmagnesium-ferrosilicon (46.99% Si, 0.78% Al, 9.49% Mg, 0.53% Ce) in thepocket at the bottom of a ladle and covering it with ferrosiliconinnoculant (48.79% Si). Base iron in the amount of 750 lbs. was pouredonto the material in the pocket.

The metal in the ladle was cleaned of dross and the treated iron wastransferred to 250 lb. covered pouring ladles. Approximately two minuteselapsed from the time of treatment of the base metal to the transferinto the pouring ladles. After various holding times, the metal waspoured at predetermined temperatures into molds and sample castings wereprepared. Analysis data for the metal tested is shown in Table Itogether with pouring temperatures and holding times.

The holding times shown in Table I start from the time the pouringladles were filled.

TABLE I.LADLE DATA SHOWING CH SILICON, AND OTHER ADDITIONS ADDED.[Asterisk C) denotes estimated values].

Analysis} 4 percent Percent Percent S1 Added Ladle Pouring Holding MgAdded Percent Percent No. Temp Time, as Mg Re- Other C C Si 0.12. F.MinzSee Mg-Fe-Si covered As As Additions (pin) (bar) (bar) Mg-Fe-SiFe-Si 3. 97 4. 05 2. l3 4. 76 2, 700 0. 280 0. 076 1. 387 0. 245 0. 3.92 1 NR 2. 14 *4. 76 2, 4:20 23:40 0. 280 0. 047 1. 387 0. 245 0. 3. 513. 50 2.12 4. 21 2, 580 0 0. 280 0. 074 1. 387 0. 245 0. 3. 56 1 N R2.18 *4. 29 2, 300 15:30 0. 280 0.072 1. 387 0. 245 0. 3. 70 3. 56 2.*4. 38 2, 560 0 0. 280 0. 067 1.387 0. 245 0. 3. 73 1 NR 2.10 *4. 43 2,300 16:00 0. 280 0. 004 1. 387 0. 245 0. 3. G5 3. 52 2.00 *4. 32 2, 5700 O. 130 0. 048 0. 640 0.956 0,014 Bi. 3. 71 3. 61 2. 4. 31 2, 290 14:000. 130 O. 041 0. G40 0. 956 0.014 Bi.

1 NR=not reported. 2 Bismuth added in lump form.

= Pin samples for carbon analyses taken from the ladle. bon equivalentpercentage=percent C+ percent Si. 4 Typical amounts of other elementsare as follows:

' Except 13-7 and 13-8.

The castings obtained following the aforedescribed procedure wereexamined with regard to nodule count, nodule size, graphite type andpresence of carbides.

Nodule counts were obtained by projecting an image of the specimen on aground glass screen using an 8.0 X 0.20 Na objective lens; a 10Xhyperplane eyepiece; and adjusting to obtain a magnification of 200x.The number of graphite nodules greater than inch diameter on the groundglass screen was then determined in a 10 cm. x 10 cm. area. Four randomcounts were made and added to obtain the number of nodules per mm. ofsample surface area. Nodule sizes were recorded by measuring theirdiameter on the ground glass screen at 200x and converting them toactual nodule dimensions.

Graphite type was recorded as spheroidal, compact and in. diameter barsused for 0 analyses. 1% in. diameter bars used for Si analyses. Carandis readily identifiable visually at magnifications of say x; compactgraphite refers to those shapes which deviate from spheroidal by beingragged and irregular; and vermicular graphite refers to shapes varyingfrom short stubby graphite to more worm-like graphite shapes.

Carbide formation in the cast samples was observed visually.

The results of the aforedescribed observations are summarized in TablesII, III and IV. Tables VI, VII and the drawing show the test resultsobtained by preparing additional castings, with and without bismuthadditions, following substantially the same procedure as describedhereinabove.

The nodule counts in the tables includes spheroidal,

vermicular. spheroidal graphite is essentially spherical compact andvermicular shapes.

TABLE II.SUMHARY OF DATA FOR 1.0 INCH DIAMETER BAR CASTING Nodule Counta per nun. Nodule Size, rmn. 10- Graphite Shape, Percent Ladle N0.Carbides Cope Center Drag Cope Center Drag Spheroids Compact Vermicular150 154 1/2+4+7 90 10 0 CLC 162 163 so 10 0 one:

159 120 90 10 0 CAS.

181 128 20 0 CAS.

174 161 90 10 0 CAS.

152 125 I5 0 CAS.

318 259 10 0 CAS.

See footnotes at end of table V.

TABLE III-SUMMARY OF DATA FOR 1.5 INCH DIAMETER BAR CASTING Nodule Count11 per mm. Nodule Size, rmn. l0 Graphite Shape, Percent Ladle No.Carbides Cope Center Drag Cope Center Drag Spheroids Compact Vermicular80 20 0 NC. 80 20 0 CLO 5O 50 0 CAS. 20 75 5 CAS. (i0 40 0 CAS. 20 75 5CAS. 85 15 0 NC. 50 50 0 Trace.

See footnotes at end of table V:

TABLE IV.-SUMMARY OF DATA FOR 2.0 INCH DIAMETER BAR CASTING N oduleCount 8 per mm. Nodule Size, mm.X10 Graphite Shape, Percent Ladle No.

Cope Center Drag Cope Center Drag Spheroids Compact Vermicular Carbideso 78 106 1+3/11 3/8 75 25 NO. 47 48 3 1/2+6/8 20 80 0 NC.

104 114 10 85 5 CAS. 99 107 20 76+ 5- NC. 101 106 80 10 CAS.

See footnotes at end of Table V.

TABLE V.SUMMARY OF DATA FOR THE 2.5 INCH DIAMETER BAR Nodule Count permm. Nodule Size, M6" units at 200X Graphite Shape, Percent Ladle No.

Cope Center Drag Cope Center Drag Spheroids Compact Vermicular Carbides0 54 39 50 50 0 NC. 47 46 20 80 0 NC. 48 5 20 GAS. 57 51 20 0 NC. 69 5715 75 10 CLC. 89 115 15 0 NC. 73 79 50 50 0 NC.

Nodule counts include all graphite shapes over 5 16 inch diameter whenviewed at 200x.

Nodule size is represented by values indicating the approximate diameterof the graphite shape. A value of 2/6 is read as diameters ranging from2 to 6. A value of 2+4 indicates two separate sizes of graphite shapes.

TABLE VI (refer to drawing) .EFFECT OF ADDITION, POURING TEMPERATUR EACHGRAPHITE SHAPE Designations in carbides column are read as follows:

N C =N 0 carbides. Trace=Trace of carbides at center. CLC Centerlinecarbides. C1/2R= Cai'bides in center 1/2 radius. C2/3R= Carbides incenter 2/3 radius. CAS Carbides across section.

E AND SECTION SIZE ON PERCENTAGE OF 0.14% Mg Added 0.14% Mg Added plus0.28% Mg Added 0.01% Bi Added Chemical Bar Diam. Analysis (in.)

Poured Hot Poured Cold Poured Hot Poured Cold Poured Hot Poured Cold(2,5l52,700 F.) (2,3002,475 F.) (2,5l52,700 F.) (2,3002.475 F.)(2,5152,700 F.) (2,3002,475 F.)

4.31-4.43% 0.13 Figure 1 .1 Figure 2 Figure 3 Figure 4 Figure 5 Figure6.

TABLE VII.EFFECT OF ADDITIONS, POURING TEMPERATURE, AND SECTION SIZE ONCARBIDE FORMATION* 0.14% Mg Added 1 0.14% Mg Added plus 0.28% Mg Added 10.015% Bi Added Chemical Bar Diam. Analysis (in) Poured Hot Poured ColdPoured Hot Poured Cold Poured Hot Poured Cold (2,5152,700 F.)(2,3002,475 F.) (2,515-2,700 F.) (2,3002,475 F.) (2,5152,700 F.)(2,300--2,475 F.)

1. 0 CAS. 431M371 $33 Nu jiijjjjjijij Si 2. 5 N C CLC 1 Nominal amounts.*Designations for carbide formation are as follows:

NC No carbides.

Trace=Trace of carbides at center. CLC Centerline carbides.

C1/2R=Carbides in center 1/2 radius. C2l3R=Carbides in center 2/3radius. CAS=Carbides across section.

As can be seen from the data in the tables, the metal 60 muth inaccordance with the present invention can be treated with bismuth inaccordance with the present invention (B7 and B8) exhibit an overallsuperiority as compared to the other irons.

For example, the bismuth treated iron, as shown in Tables II-V have, onthe average, 50 to more nodules than the other irons. Also, as shown inTables II-V, carbide formation and vermicular graphite are essentiallyeliminated from the bismuth treated irons.

Table VI in conjunction with the drawing further graphically illustratesthat bismuth treated irons can be poured cold and provide, on theaverage, higher amounts of spheroidal graphite. The advantage of thebismuth treatment is particularly pronounced for the larger diametercastings.

Table VII further illustrates that iron treated with bis- (c) carbidesare substantially prevented due to the in- 75 creased number of graphitespheroids precipitated.

Further, irons of 4.3 carbon equivalent and under can be castsubstantially without the formation of undesirable graphite shapes andundesirable graphite shapes and carbides are avoided even in largercasting section thicknesses.

What is claimed is:

1. In a process for making nodular iron by bringing together magnesium,silicon and molten iron, the improvement which comprises providing inthe molten iron a silicon content of between about 1 to 5%, a magnesiumaddition of about 0.02 to 0.25% and a bismuth addition of from about0.010 to about 0.050%, said bismuth addition being sufiicient toprovidea substantial increase in the amount of spheroidal graphite nodules inthe iron as compared to the same iron without a bismuth addition. p

2. An improved process in accordance with claim 1 wherein the bismuthaddition is in the range of about 0.010 to about 0.015%.

References Cited by the Examiner UNITED STATES PATENTS 2,485,760 10/1949Millis et al. 75-130 2,536,204 1/ 1951 Morrogh et al. 75l30 X 2,579,45212/1951 Eckman et al. -75130 X 2,780,541 2/1957 Zifferer 75130 2,841,4907/1958 Steven 75-130 2,943,932 7/1960 White et al. 75-130 X DAVID L.RECK, Primary Examiner.

HYLAND BIZOT, H. W. TARRING,

Assistant Examiners.

1. IN A PROCESS OF MAKING NODULAR IRON BY BRINGING TOGETHER MAGNESIUM,SILICON AND MOLTEN IRON, THE IMPROVEMENT WHICH COMPRISES PROVIDING INTHE MOLTEN IRON A SILICON CONTENT OF BETWEEN ABOUT 1 TO 5%, A MAGNESIUMADDITION OF ABOUT 0.02 TO 0.25% AND A BISMUTH ADDITION OF FROM ABOUT0.010 TO ABOUT 0.050%, SAID BISMUTH ADDITION BEING SUFFICIENT TO PROVIDEA SUBSTANTIAL INCREASE IN THE AMOUNT OF SPHEROIDAL GRAPHITE NODULES INTHE IRON AS COMPARED TO THE SAME IRON WITHOUT A BISMUTH ADDITION.